This disclosure is directed to skeletal bone fixation systems, and more particularly to a fixation assembly for vertebrae of a spinal column.
Spinal fixation systems are used to secure sections of the spinal column, such as vertebral bodies, into a fixed position to correct spinal injuries and defects. Internal fixation is used most frequently in the spine in conjunction with vertebral fusion, and also for the manipulation of the spine to correct spinal deformities. A typical spinal fixation assembly includes a fixation device, such as a screw or hook, that can be attached to a portion of a first vertebral body. The screw can be coupled to a stabilization member, such as an elongate rod, that can be linked to one or more additional vertebral bodies using additional screws.
Pursuant to a general process, two or more bone screws and/or hooks are secured to a vertebral body that is to be stabilized. After the screws are secured to the vertebral bodies, the screws are coupled to a spinal stabilization rod that restricts movement of the stabilized vertebra. It is important that the screws have a secure coupling with the spinal stabilization rod in order to prevent movement of the rod relative to the screw after placement.
In several available pedicle screw systems, a tulip-like coupling element with opposing upright arms or walls is used to secure the pedicle screw to the rod. The coupling element and pedicle screw are configured to be coupled to an elongate stabilizer, such as a rod, that is positioned above the head of the pedicle screw. A compression member, such as a compression nut, is configured to mate with the coupling element and provides a compressive force to the rod. The rod is then forced against the head of the pedicle screw, and that force is translated to the coupling element. Accordingly, the forces generated by the compression nut clamp the rod and pedicle screw head together within the coupling element.
One type of pedicle screw system is a bottom-loaded system wherein the screw is loaded into the coupling element through the bottom of the coupling element. Bottom loading can allow for greater flexibility and adjustment of the coupling element relative to the screw. There is a need for improved bottom-loaded pedicle screw systems.